Seat construction

ABSTRACT

A flat spring member ( 40 ) mainly serving as a vibration absorptive function at a normal use is engaged with a supporting frame member ( 130 ) which displaces backward along with deformation of a seat back ( 20 ) by backward moment applied to the seat back ( 20 ), and the other end is engaged with a front edge frame ( 102 ) disposed in the vicinity of the front edge of a cushion frame. Therefore, when an impact force from front or back equal to or more than that prescribed is applied, the flat spring member ( 40 ) increases in tension by backward moment applied to the seat back ( 20 ), and serves as a function to increase again the intensity of the backward moment of the seat back ( 20 ), which was once lowered by deformation of the side frame ( 101 ) of the cushion frame.

FIELD OF THE INVENTION

The present invention relates to a seat structure, more in detail, to aseat structure suitable for transportation machines such as a plane, atrain, a ship, a fork lift, an automobile and the like, or for variouschairs and a wheel chair used inside or outside of a building.

BACKGROUND OF THE INVENTION

In a seat used in a plane, a train, a ship, an automobile and the like,a seat back is required to be tilted not more than necessity when alarge impact force is applied upon a head-on collision or a rear-endcollision. When a seat back tilts too deep, a passenger on a back seatmay be injured. It is also conceivable that the leg is caught in asteering, which may cause a risk to receive an injury by a load on thewaist or the like or receive an injury on the head by baggage put on theback seat. Therefore, it is required to restrain a tilt of a seat backto restrain displacement of the human body by pushing the passenger'sback to a cushioning material disposed on a back frame so as to increaseabsorbency of impact. Hitherto, various countermeasures to increaseyield strength (the backward moment strength) against such a backwardrotation moment applied to the seat back have been proposed. However,most of them relate to improvement of a seat frame structure, and evenwhen such an improved seat frame is used, development of technologycapable of increasing the intensity of the backward moment has beenstill required.

The present invention has been made in view of the above problems and anobject of the present invention is to provide a seat structure capableof increasing intensity of the backward moment more than before so thatthe impact resistance can be further improved even when a seat framedesigned to reduce in weight is used.

SUMMARY OF THE INVENTION

In recent years, the present inventor has been proposed a seat structurein which a three-dimensional net member (solid knitted fabric) having athickness of several millimeters to several tens millimeters is strainedon a seat frame. According to this seat structure, since thisthree-dimensional net member has a tension structure, it has acharacteristic that it can be provided with a sufficient vibrationabsorptive function as a seat structure for a transportation machineowing to a damping function of the tension structure by supporting itvia a spring mechanism as well as its being light in weight. However,various spring mechanisms used here are to serve mainly as a vibrationabsorptive function and do not positively possess a function to serve asa high-impact material capable of resisting against impact force fromfront or back equal to or stronger than that prescribed due to a head-onor rear-end collision. Even in such a structure, increase in theintensity of the backward moment as described above is mainly achievedwith a seat frame structure. The present inventors have noted astructure in which a spring mechanism and a damping mechanism used toabsorb vibration in normal times are forced to effectively operate as ahigh-impact material to increase the intensity of the backward momentalong with the seat frame structure when received an impact force fromfront or back due to a head-on or rear-end collision, thereby exhibitingthe backward moment larger in intensity than in the case of having thesame seat frame structure.

In one embodiment of the present invention, a seat structure includes aflat spring member disposed in such a manner that one end thereof is inengagement with a frame member to be displaced backward by backwardmoment, which deforms a seat back under an impact force from front orback equal to or stronger than that anticipated. Another end is inengagement with a frame member disposed in the vicinity of the frontedge of a cushion frame, wherein the flat spring member increases intension as the seat back is deformed.

In another embodiment of the present invention, a seat structureincludes a cushion frame with a frame member deforming under an impactforce from front or back equal to or stronger than that anticipated, anda flat spring member is disposed in such a manner that one end thereofis in engagement with a frame member to be displaced backward along withdeformation of a seat back by backward moment applied to the seat back.Another end is in engagement with the frame member disposed in thevicinity of the front edge of the cushion frame, wherein the flat springmember increases in tension accompanied by deformation of the seat backto perform a function to increase the intensity of the backward momentof the seat back.

In a further embodiment of the seat structure of the present invention,the frame member engaged with one end of the flat spring member anddisplacing backward by the backward moment toward the seat back includesa frame member comprising a back frame.

In a further embodiment of the seat structure of the present invention,the frame member engaged with one end of the flat spring member anddisplacing backward by the backward moment toward the seat back includesa frame member elastically supported in an independent state from theback frame, and provided at a position corresponding to the vicinityfrom the haunches to the waist of a driver, along the width direction ofthe seat.

In a further embodiment of the seat structure of the present invention,the frame member displacing backward by backward moment toward the seatback includes a frame member comprising the cushion frame, and issupported by an arm biased in a direction of backward tilt under anormal state by means of a torsion bar disposed along the widthdirection at a position to be deformed by an impact force equal to orstronger than that anticipated to the seat back.

In a further embodiment of the present invention, the seat structurefurther includes a stopper to control deformation of the cushion frameand the back frame under an impact force from front or back equal to orstronger than expected.

In a further embodiment of the seat structure of the present invention,the flat spring member includes one kind selected from a two-dimensionalnet member and a three-dimensional net member (solid knitted fabric) ora combination of two kinds or more thereof.

In a further embodiment of the seat structure of the present invention,a cushioning member includes one kind selected from a two-dimensionalnet member, a three-dimensional net member and a urethane material or acombination of two kinds or more thereof, and is disposed above saidflat spring member in such a manner that one end thereof is inengagement with the frame member to be displaced backward along withdeformation of the seat back by backward moment applied to the seat backand the other end is in engagement with a frame member disposed in thevicinity of the front edge of the cushion frame.

In a further embodiment of the seat structure of the present invention,the cushioning member includes a three-dimensional net member (solidknitted fabric) formed by connecting two layers of front and back of theground knitted fabrics with connecting yarn.

In a further embodiment of the present invention, the seat structurefurther includes a portion without connecting yarn at an arbitraryposition between one end and the other end of the three-dimensional netmember where no connecting yarn is provided and the ground knittedfabrics directly face each other.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic side elevational view showing a main portion of aseat structure relating to an embodiment of the present invention, beingin a state before an impact force equal to or stronger than thatprescribed is applied;

FIG. 2 is a schematic side elevational view showing a main portion ofthe seat structure relating to an embodiment of the present invention,being in a state after the impact force equal to or stronger than thatprescribed is applied;

FIG. 3A is a sectional view taken along an arrow A in FIG. 1, and FIG.3B is a sectional view taken along an arrow B in FIG. 2;

FIGS. 4A, 4B and 4C show desirable examples of a three-dimensional netmember (solid knitted fabric) used for a cushioning member, in whichFIG. 4A shows the solid knitted fabric being strained on a seat framebefore an impact force equal to or stronger than that prescribed beingapplied, FIG. 4B is a view showing a structure of a ground knittedfabric on the back side, and FIG. 4C shows a structure of the groundknitted fabric on the front side;

FIG. 5 is a view showing a solid knitted fabric in a state after animpact force equal to or stronger than that prescribed is applied;

FIG. 6 is a view showing an example of a measurement result of theintensity of the backward moment;

FIG. 7 is a view showing another example of a measurement result of theintensity of the backward moment;

FIG. 8 is a view showing tensile properties of a two-dimentional netmember used as a flat spring member;

FIG. 9 is a view showing an appearance in a no-load state, whensupported by a supporting frame which is biased backward together withthe cushioning member and a flat spring member by a torsion bar; and

FIG. 10 is a view showing the cushioning member in a state of beingseated by a person.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be explained in more detail based onembodiments shown in the drawings. FIGS. 1 and 2 are views showing amain portion of a seat structure relating to an embodiment of thepresent invention. As shown in these drawings, a seat cushion 10 and aseat back 20 forming the seat structure of the present embodimentinclude a cushion frame 100 and a back frame 200 respectively.

The cushion frame 100 is formed with a plurality of frame members suchas side frames 101 disposed apart from and opposite to each other in thewidth direction, a front edge frame 102 disposed between both front endsof the side frames 101 and the like so as to form nearly a square or theshape of a letter U seen from the top as a whole. To the side frame 101,a fixing bracket 103 is fixed along the bottom edge thereof and the sideframe 101 is slidably supported by a rail 111 which forms a slideadjuster 110 via the fixing bracket 103.

The side frame 101 which is one of the frame members of the cushionframe 100 deforms by a backward rotation moment (backward moment)against the seat back 20 (back frame 200), when an impact force equal toor stronger than that prescribed is applied in the longitudinaldirection due to a head-on or rear-end collision as shown in FIG. 2. Dueto such deformation of the side frame 101, the intensity of the backwardmoment of the seat back 20 is varied. In order to relieve the impactcaused by the deformation at this time, a bead portion 101 a which isbent to bulge outward is formed in the side frame 101, as shown in FIG.1 and FIG. 3A, in the vicinity of the upper end edge of the side frame101, at the position a little close to the back end from the central inthe longitudinal direction. Through this structure, when an impact forceequal to or stronger than that prescribed is applied to the seat back 20as described above, the side frame 101 bends downward from the middle inthe longitudinal direction with respect to the rail 111 of the slideadjuster 110 by the backward moment. At this time, since the beadportion 101 a stretches in the longitudinal direction as shown in FIGS.2 and 3B, proceeding of rupture of the side frame 101 is restrained sothat the impact is relaxed.

A first bracket 104 is connected to the rear end of the side frame 101of the cushion frame 100. The first bracket 104 is connected to a secondbracket 201 via a reclining adjuster 30. The second bracket 201 is fixedto the bottom end of a back frame 200. Accordingly, the back frame 200is provided so as to be able to recline with respect to the cushionframe 100 via the reclining adjuster 30. It should be noted that in thepresent embodiment, the first bracket 104 constitutes a portion of thecushion frame 100, and the second bracket 201 constitutes a portion ofthe back frame 200. It is needless to say that in the case of astructure without the reclining adjuster 30, the first bracket 104 andthe second bracket 201 are directly connected with bolts or the like.

A projecting plate (not shown) projecting inward is provided in thefirst bracket 104 which constitutes the cushion frame 100 and is fixedat the rear end of the side frame 101, and a bracket for disposing thetorsion bar 105 is fixed to the projecting plate so that the bracket 105projects downward.

The brackets 105 for disposing the torsion bar 120 are provided on eachside frame 101 disposed apart from each other at a prescribed distancein the width direction of the cushion frame 100, one end portion (fixedend) of a torsion bar 120 is fitted to a hole formed in one of thebrackets 105 for disposing the torsion bar 120, and the other endportion (free end) of the torsion bar 120 is rotatably supported in ahole of the other bracket 105 for disposing the torsion bar 120.Accordingly, the torsion bar 120 is provided along the width directionof the seat cushion 10 or the cushion frame 100, and exhibits aprescribed spring characteristic by twisting of the free end side.

An arm 121 is fixed in the vicinity of each end portion of the torsionbar 120. One of the arms 121 disposed on the fixed end side of thetorsion bar 120 is pivotably disposed to the torsion bar 120 at the baseend portion thereof, and the other arm 121 disposed on the free end sideof the torsion bar 120 is directly connected to the torsion bar 120 atthe base end portion thereof, and is biased in a direction of backwardtilt by twist torque thereof. A supporting frame 130 is disposed betweenthe upper end portions of respective arms 121. Accordingly, thesupporting frame 130 is elastically supported so as to be biased in adirection of backward tilt under a normal state by the springcharacteristic of the torsion bar 120 via the arm 121.

The supporting frame 130 is used for a frame member to engage with oneend 41 of a flat spring member 40. The other end 42 of the flat springmember 40 is engaged with the front edge frame 102 which is one of theframe members to compose the cushion frame 100. Accordingly, while theflat spring member 40 is supported by the front edge frame 102 at theother end 42, since one end 41 is biased backward by an elastic force ofthe torsion bar 120, the flat spring member 40 is strained in thelongitudinal direction of the seat cushion 10 at a prescribed tension.

As a result that the flat spring member 40 is strained at a prescribedtension as described above, vibration in a usual range inputted in thedirection of the normal can be dispersed in the facial direction so thatthe vibration can be effectively absorbed. In the case of the presentembodiment, the flat spring member 40 is elastically supported by thetorsion bar 120 via the supporting frame 130 and the arm 121. In otherwords, the torsion bar 120 biases the supporting frame 130 in adirection of backward tilt via the arm 121 as described above to strainthe flat spring member 40, and the initial tension is adjusted so thatthe supporting frame 130 (arm 121) takes an unstably balanced positionin an equilibrium state at the time of being seated. As a result, itbecomes possible to react sensitively to a very little vibration, and atthe same time, a firm feeling of stroke can be created owing torestorative power of the torsion bar 120. Especially, since the torsionbar 120 can create a well-balanced state, operating effectively therestorative power to displacement from no-load state to an equilibriumstate, it has a high vibration absorptive function. Incidentally, thefunctions of the flat spring member 40 and the torsion bar 120 at thetime when an impact force equal to or stronger than that prescribed isapplied in the longitudinal direction by a head-on or rear-end collisionwill be described later.

Considering the object of the present invention, while the flat springmember 40 needs to be fixed in such a manner that it supplements animpact-resistant function exhibited by deformation of the seat frame(the cushion frame 100 and the back frame 200) to enhance impactresistance of the seat structure when an impact force equal to orstronger than that prescribed is applied in the longitudinal direction,it also needs to exhibit a sufficient vibration absorptive function evenfor a vibration usually inputted as described above. Though the flatspring member 40 is not to be limited so far as it is provided with sucha function, the following member is used in the present embodiment.

That is, the flat spring member 40 used in the present embodimentincludes elastic yarn, either of the warp or the weft is composed ofelastic yarn such as-polyester elastomer fiber, polyurethane fiber orthe like, and the other is composed of common yarn such as nylon fiber,polyester fiber or the like, which is smaller in elasticity than theelastic yarn. And desirably, as shown in FIG. 8, the flat spring member40 should display a softening spring characteristic as tensilecharacteristics when pulled along the arrangement direction of theelastic yarn, and display a linear spring characteristic as tensilecharacteristics when pulled along the arrangement direction of thecommon yarn. When the flat spring member 40 is kept stretching by beingapplied an impact force equal to or more than that prescribed in thelongitudinal direction, and the common yarn is finally ruptured, dampingratio can be increased by the softening spring characteristics. Itshould be noted that, as shown in FIG. 8, as for linear springcharacteristics when pulled along a roll direction of the fabricmaterial, which is the direction of common yarn arrangement, it ispossible to have a structure without non-linear characteristics at allas is seen from roll direction 1, or a structure having non-linearcharacteristics in an initial bending region (a region in amount ofbending to be usually 10 mm or less (roll direction 2) or 20 mm or lessat maximum (roll direction 3)) by selecting materials or yarn diameterof the common yarn or the like. By taking a structure having non-linearcharacteristics in the initial bending region, a feeling of stroke atthe time of being seated can be increased. Incidentally, the tensilecharacteristics shown in FIG. 8 are obtained by measuring in such amanner that using a test piece cut from the above-describedtwo-dimensional net member in 200 mm long and 50 mm width, the testpiece is pulled along the longitudinal direction at a rate of 50 mm/minby a test machine while taking a portion from each end in thelongitudinal direction to 50 mm inside of the test piece as a margin forgripping. At this time, for the tensile characteristics along thearrangement direction of the elastic yarn, a test piece cut in such amanner that the arrangement direction of the elastic yarn being alongthe longitudinal direction is used, while for the tensilecharacteristics along the arrangement direction of the common yarn, atest piece cut in such a manner that the arrangement direction of thecommon yarn being along the longitudinal direction is used.

According to the seat structure of the present embodiment, at the timeof normal use, absorption of vibration is achieved by the operation ofthe flat spring member 40 and the torsion bar 120 as described above. Onthe contrary, when an impact force equal to or stronger than thatprescribed is applied in the longitudinal direction by a head-on orrear-end collision, since the human body is restrained by a seat belt orthe like, a big load is generated in a direction of tilting the seatback 20 backward in any case. By a backward moment to tilt the seat back20 in the backward turning direction, as shown in FIG. 2, the side frame101 of the cushion frame 100 is deformed to bend downward at anarbitrary position from the vicinity of nearly central portion to thevicinity of the rear end, and around the position lower than theposition where the flat spring member 40 is disposed in a normal state.At this time, the bead portion 101 a provided in the vicinity of upperend edge of the side frame 101 stretches in the longitudinal directionas shown in FIG. 3B so that proceeding of rupture of the side frame 101is restrained.

When the side frame 101 is deformed, the fixing bracket 103 whichsupports the side frame 101 on the rail 111 of the slide adjustor 110similarly bends. In this event, since the amount of deformation of theside frame 101 is larger due to a difference in strength between theside frame 101 and the fixing bracket 103, the bottom end of the firstbracket 104 integrally connected to the rear end of the side frame 101abuts a rear end portion 103 a of the fixing bracket 103 to temporarilyrestrain the deformation of the side frame 101. Accordingly, the rearend portion 103 a of the fixing bracket 103 serves a function as astopper to restrain the deformation of the side frame 101.

At this time, the intensity of the backward moment which is yieldstrength against a backward turning direction of the back frame 200gradually increases after receiving a prescribed impact force, as shownin FIG. 6, and at a point of A, the side frame 101 of the cushion frame100 and the back frame 200 start deforming. Then, inclination inintensity of the backward moment slightly changes from the point A. Whenthe flat spring member 40 is not provided, change in the intensity ofthe backward moment is greatly reduced at this time. However, accordingto the present embodiment, as the cushion frame 100 deforms, tension ofthe flat spring member 40 increases along with backward displacement ofthe back frame 200 to further increase the intensity of the backwardmoment. A point “B” is a point where deformation due to stretching ofthe bead portion 101 a at the maximum or generation of cracks startsappearing as described above, and the intensity of the backward momentstarts lowering from the point B. Since deformation of the side frame101 is restrained when the side frame 101 abuts the rear end portion ofthe fixing bracket 103, tension of the flat spring member 40 greatlyworks from the time of abutting (point C) and the intensity of thebackward moment starts to increase again. When deformation of the sideframe 101 further proceeds, the intensity of the moment starts loweringagain from a point D due to generation of a crack in the beat portion101 a stretched at the maximum or enlargement of the crack previouslygenerated, but since tension of the flat spring member 40 becomes large,the intensity of the backward moment turns to increase again from pointE.

Due to the deformation of the side frame 101 as described above, theintensity of the backward moment of the back frame 200 changes asdescribed above. Previously, while the intensity of the backward momentof the back frame 200 is kept at a prescribed criterion by such adeformation behavior of the seat frame, during which the vicinity fromthe haunches to the waist of a human body pushes a thin cushioningmember such as a solid knitted fabric or the like strained on the backframe 200 to allow it to operate as if buried into the back frame 200 sothat the reaction of the human body is restrained. However, there is alimit, because this impact absorption mechanism utilizes onlydeformation behavior of the seat frame.

On the contrary, according to the present embodiment, when deformationof the side frame 101 proceeds and bending downward is going on asdescribed above, since the bracket for disposing the torsion bar 105which is fixed to the side frame 101, displaces also in a downwardslanting direction, the arm 121 tilts backward along with displacementof the back frame 200 in a direction of backward tilt so that thesupporting frame 130 is displaced backward. Since one end of the flatspring member 40 is supported by the supporting frame 130 and the otherend of the flat supporting member 40 is engaged with the front edgeframe 102, tension of the flat spring member 40 becomes high.Accordingly, as described above, even when inclination of the intensityof the backward moment is changed due to enlargement of the deformationof the side frame 101, since tension of the flat spring member 40 isincreased as the amount of deformation of the side frame 101 and theamount of deformation of the back frame 200 in a direction of backwardtilt are enlarged in the case of the present embodiment, the intensityof the backward moment can be enhanced by the tension of the flat springmember 40. As a result, tilting of the seat back 20 is restrained, andthe back of a human body is supported by a cushion member such as asolid knitted fabric strained by the back frame 200 more reliably thanby the prior art. In other words, in the present embodiment, the flatspring member 40 performs mainly vibration absorptive function in normaltimes, but when a large impact force as described above is inputted, itfunctions as a high-impact resistant material to enhance the intensityof the backward moment of the back frame 200.

FIG. 7 shows the intensity of the backward moment measured whiledisposing the flat spring member 40 similarly to the above, to a seatframe structure in which material of a little higher strength than thematerial used in the test in FIG. 6 is used as respective frame membersto compose the cushion frame 100 and the back frame 200, without using astopper for stopping deformation of the cushion frame 100 such as therear end portion 103 a of the fixing bracket 103 described above.

As shown in FIG. 7, in the case of this example, deformation occurs tothe cushion frame 100 and the back frame 200 at point F, and thereafterthe function of tension of the flat spring member 40 is added to createthe intensity of backward moment of more than 3000 Nm. Then, a largedeformation of the cushion frame 100 or the back frame 200, or stretch,crack, or the like in the bead portion occurs, which lowers theintensity of the backward moment at point G, but the tension of the flatspring member 40 becomes high again, and the intensity of the backwardmoment increases again from point H. When deformation of the cushionframe 100 and the back frame 200, cracks, or the like becomes largeagain, the intensity of the backward moment begins to lower again frompoint I, and it begins to increase again by tension increase of the flatspring member 40 when arriving at point J.

In the case of relying on the intensity of the cushion frame 100 or theback frame 200, it is not easy to attain the intensity of the backwardmoment to be equal to or more than 3000 Nm. If such a structure isrealized, it is expected to be considerably heavy. However, by addingthe flat spring member 40 as a high-impact material as in the presentembodiment, it is found it easy to attain the intensity of the backwardmoment to be equal to or more than 3000 Nm. As for the cushion frame 100or the back frame 200, it is enough to select the one being a littlehigh in strength, so that a structure having high intensity of thebackward moment being light in weight can be realized.

Note that the measurement of the intensity of the backward moment shownin FIGS. 6 and 7 is carried out in either case by setting a designed hippoint (H. P) of an apparatus in which a loading jig is provided to aback pan of a three-dimensional mannequin to a designated seatingposition on the seat structure, and applying a backward load (at aloading speed of 0.5 deg/s) to generate a moment of 588 Nm/person aroundH. P to the seat back.

The cushioning members of urethane material or a solid knitted fabricare disposed above the flat spring members 40 provided on the cushionframe 100 and the back frame 200 respectively. It is needless to saythat these cushioning members are sometimes used as a surface materialalso with themselves or they may be further covered with another surfacematerial such as a leather.

It is desirable to use a solid knitted fabric 400 as shown in FIGS. 4and 5 as a cushioning member. The solid knitted fabric 400 is formed byallowing connecting yarn 430 to reciprocate between two layers of frontand back ground knitted fabrics 410 and 420 disposed apart from andopposite to one another to connect both. The solid knitted fabric 400 islight in weight and air-permeable, and has a sufficient function as acushioning member even with the thickness of about several millimetersto several tens millimeters due to a restoring force by a tilt of theconnecting yarn 430, friction between connecting yarn 430, frictionbetween connecting yarn 430 and yarn composing the ground knittedfabrics 410 and 420, and deformation of meshes of the ground knittedfabrics 410 and 420.

The ground knitted fabric 410 used for a back layer is, for instance asshown in FIG. 4B, formed with a flat knitted structure (small mesh)continuing in any directions of wale and course from yarn twined ofmonofilaments. On the other hand, the ground fabric 420 used for a frontlayer is formed in a stitch structure having a honeycomb (hexagonal)mesh from yarn twined of monofilaments as shown in FIG. 4C. Needless tosay, this knitted fabric structure is just an example, and a meshstructure or a knitted fabric structures except a honeycomb structurecan be adopted. The connected yarn 430 is used for knitting between thepair of the ground knitted fabrics 410 and 420, so that the groundknitted fabric 420 being the front layer and the ground knitted fabric410 being the back layer can maintain a prescribed distance to giveprescribed stiffness to the solid knitted fabric 400.

When the above-described solid knitted fabric 400 is strained on thecushion frame 100 is provided, as shown in FIG. 4A, by engaging thefront end with the front edge frame 102, and the rear end is engagedwith a bottom frame 202 provided at the lower part of the back frame 200for instance. Incidentally, though not shown, the side edge portion isengaged with the side frame 101. It is desirable that the solid knittedfabric 400 provided on the cushion frame 100 is not provided withconnecting yarn 430 in a portion thereof, as shown in FIGS. 4A, 4B and4C, and of a structure including a portion without connecting yarn 440where the ground knitted fabrics 410 and 420 directly face each other.

In the case of using such a solid knitted fabric 400, when the cushionframe 100 and the back frame 200 reach a state shown in FIG. 2 from astate shown in FIG. 1 under application of an impact force equal to ormore than that prescribed in the longitudinal direction, since thebottom frame 202 displaces rearward, more correctly in a rearwardslanting direction, the solid knitted fabric 400 stretches in thelongitudinal direction as shown in FIG. 5 from a state shown in FIG. 4A.As a result, the tension of the solid knitted fabric 400 in thelongitudinal direction is enhanced to serve as a function tosupplementary further increase the intensity of the backward momentincreased by the tension of the above-described flat spring member 40.

However, in the case of a structure having no portion without connectingyarn 440, the ground knitted fabrics 410 and 420 stretch and theconnecting yarn 430 tilts at the same time, the total thickness becomesthinner, which heightens the surface stiffness in the thicknessdirection (direction of the normal) to lower the cushioning ability inthe direction of the normal. On the contrary, in the case of a structureincluding the portion without connecting yarn as in the presentembodiment, since positions directly facing each other in the portionwithout connecting yarn 440 is to be intensively stretched, between theground knitted fabrics 410 and 420, as shown in FIG. 5, the connectingyarn 430 disposed in positions other than the portion without connectingyarn 440 do not tilt so much, and keep nearly the same state as thatbefore the impact force is applied. As a result, lowering of the impactforce in the direction of the normal accompanied by the stretch in thelongitudinal direction is restrained, so that a relieving function ofthe impact force generated especially in the vertical direction can beenhanced when an impact force is applied.

The solid knitted fabric 400 described above is disposed above the flatspring member 40, but it is also possible to use the solid knittedfabric 400 itself as a flat spring member 40, and to engage the rear endof the solid knitted fabric 400 with the supporting frame 130 supportedby the torsion bar. Even in this case, by making it a structure to beprovided with the portion without connecting yarn 430, the groundknitted fabrics 410 and 420 at a position corresponding to the portionwithout connecting yarn 440 are stretched, thereby restrainingdeformation of the cushion frame 100 and the back frames 200, exhibitinga function to enhance the intensity of the backward moment of the seatback 20, restraining excessive tilt of the connecting yarn 430, andmaking the cushioning ability in the vertical direction exhibitsufficiently.

As shown in FIG. 9, it is also possible to adopt a structure in whichone end 41 of the flat spring member 40 and the rear end of the solidknitted fabric 400 are engaged together with the supporting frame 130supported by the torsion bar. In this case, since the supporting frame130 is biased in the direction backward tilt by an elastic force of thetorsion bar at the time of no load, the solid knitted fabric 400strained on the front sides shows an appearance without needless shrinksand folds. On the other hand, when a person is seated, since thesupporting frame 130 is tilted forward as shown in FIG. 10, the solidknitted fabric 400 does not increase in tension but creates slack.Therefore, the cushioning ability in the thickness direction included inthe solid knitted fabric 400 can be exhibited sufficiently. It should benoted that it is desirable to use the solid knitted fabric 400 asdescribed above, it is also possible to use comparatively thin urethanematerial.

INDUSTRIAL APPLICABILITY

A seat structure of the present invention has a structure in which aflat spring member mainly serving as a vibration absorptive function ata normal use is engaged with an arbitrary frame member which displacesbackward along with deformation of a seat back by backward momentapplied to the seat back, and the other end is engaged with a framemember disposed in the vicinity of the front edge of a cushion frame.Therefore, when an impact force from front or back equal to or more thanthat prescribed is applied, the flat spring member increases in tensionby backward moment applied to the seat back, and serves as a function toincrease the intensity of the backward moment of the seat back.Therefore, according to the present invention, high intensity of thebackward moment can be exhibited compared with that in the prior art sothat further improvement of the impact resistance can be realized.

1. A seat structure, comprising: a flat spring member disposed in such amanner that one end is in engagement with a first frame member to bedisplaced backward by backward moment, which deforms a seat back underan impact force from front or back, and the other end is in engagementwith a second frame member disposed in the vicinity of the front edge ofa cushion frame, wherein the flat spring member increases in tension assaid seat back is deformed and wherein the first frame member is engagedwith one end of said flat spring member and displacing backward by thebackward moment toward said seat back wherein the first frame member iselastically supported in an independent state from the back frame, andprovided at a position corresponding to the vicinity from a driver'shaunches to the driver's waist, along the width direction of the seat.2. The seat structure according to claim 1, wherein the first framemember engaged with one end of said flat spring member and displacingbackward by the backward moment toward said seat back includes a framemember comprising a back frame.
 3. The seat structure according to claim1, further comprising: a stopper to control deformation of the cushionframe and back frame under an impact force from front or back equal toor stronger than that prescribed.
 4. The seat structure according toclaim 1, wherein said flat spring member comprises one kind selectedform a two-dimensional net member and a three-dimensional net member ora combination of two kinds or more thereof.
 5. The seat structureaccording to claim 1, wherein said cushion member comprises one kindselected from a two-dimensional net member, a three-dimensional netmember and a urethane material or combination of two kinds or morethereof, and is disposed above the flat spring member in such a mannerthat one end thereof is in engagement with the first frame member to bedisplaced backward along with deformation of the seat back by backwardmoment applied to the seat back and the other end is in engagement witha second frame member disposed in the vicinity of the front edge of thecushion frame.
 6. The seat structure according to claim 5, wherein saidcushioning member comprises a three-dimensional net member formed byconnecting two layers of front and back of ground knitted fabrics withconnecting yarn.
 7. The seat structure according to claim 6, furthercomprising: a portion without connecting yarn at the arbitrary positionbetween one end and the other end of said three-dimensional net memberwhere no connecting yarn is provided and the ground knitted fabricsdirectly face each other.
 8. A seat structure, comprising: a cushionframe provided with a frame member deforming under an impact force fromfront or back; and a flat spring member disposed in such a manner thatone end thereof is in engagement with a first frame member to bedisplaced backward along with deformation of a seat back by backwardmoment applied to said seat back, and the other end is in engagementwith a second frame member disposed in the vicinity of the front edge ofthe cushion frame, wherein the flat spring member increases in tensionaccompanied by deformation of said seat back to perform a function toincrease the intensity of the backward moment of the seat back andwherein the first frame is displaced backward by backward moment towardsaid seat back is supported by an arm biased in a direction of backwardtilt under a normal state by means of a torsion bar disposed along thewidth direction at a position to be deformed by an impact force equal toor stronger than that prescribed to said seat back.
 9. The seatstructure according to claim 8, wherein the first frame member engagedwith one end of said flat spring member and displacing backward by thebackward moment toward said seat back includes a frame member comprisinga back frame.
 10. The seat structure according to claim 8, wherein thefirst frame member engaged with one end of said flat spring member anddisplacing backward by the backward moment toward said seat backcomprises a frame member elastically supported in an independent statefrom the back frame, and provided at a position corresponding to thevicinity from a driver's haunches to the driver's waist, along the widthdirection of the seat.
 11. The seat structure according to claim 10,wherein the first frame displacing backward by backward moment towardsaid seat back comprises a frame member composing said cushion frame,and is supported by an arm biased in a direction of backward tilt undera normal state by means of a torsion bar disposed along the widthdirection at a position to be deformed by an impact force.
 12. The seatstructure according to claim 8, further comprising: a stopper to controldeformation of the cushion frame and the back frame under an impactforce from front or back.
 13. The seat structure according to claim 8,wherein said flat spring member comprises one kind selected from atwo-dimensional net member and a three-dimensional net member or acombination of two kinds or more thereof.
 14. The seat structureaccording to claim 8, wherein said cushion member comprises one kindselected from a two-dimensional net member, a three-dimensional netmember and a urethane material or a combination of two kinds or morethereof, and is disposed above the flat spring member in such a mannerthat one end thereof is in engagement with the first frame member to bedisplaced backward along with deformation of the seat back by backwardmoment applied to the seat back and the other end is in engagement witha frame member disposed in the vicinity of the front edge of the cushionframe.
 15. The seat structure according to claim 14, wherein saidcushioning member comprises a three-dimensional net member formed byconnecting two layers of front and back of ground knitted fabrics withconnecting yarn.
 16. The seat structure according to claim 15, furthercomprising: a portion without connecting yarn at a position between oneend and the other end of said three-dimensional net member where noconnecting yarn is provided and the ground knitted fabrics directly faceeach other.